The present invention relates to a variable focal length lens comprising micromirrors with two degrees of freedom (DOF) rotation.
A most widely used conventional variable focal length system is the one using two refractive lenses. It has complex driving mechanisms to control the relative positions of refractive lenses and a slow response time. Alternatively, variable focal length lenses have been made. Variable focal length lenses can be made by changing the shape of the lens, as is found in the human eye; this method has been used in lenses made with isotropic liquids. Other lenses have been made of electrically variable refractive index media to create either a conventional lens or a gradient index lens by means of a voltage gradient. The electrically variable refractive index allows the focal length of the lenses to be voltage controlled. Among them, the most advanced variable focal length lens is a liquid crystal variable focal length lens, which has a complex mechanism to control the focal length. Its focal length is changed by modulating the refractive index. Unfortunately, it has a slow response time typically on the order of hundreds of milliseconds. Even though the fastest response liquid crystal lens has the response time of tens of milliseconds, it has small focal length variation and low focusing efficiency.
To solve the disadvantages of the conventional focal length lens, a fast-response micromirror array lens was proposed. The details of the fast-response micromirror array lens are described in J. Boyd and G. Cho, 2003, “Fast-response Variable Focusing Micromirror Array Lens,” Proceeding of SPIE Vol. 5055: 278–286. The paper is incorporated by reference into this disclosure as if fully set forth herein. The micromirror array lens mainly consists of micromirrors and actuating components, and uses a much simpler mechanism to control the focusing system than a liquid crystal variable focal length lens. The focal length of the micromirror array lens is varied with the displacement of each micromirror. But, the paper only describes basic idea related to design and control. Applying the micromirrors with two DOF rotations only, this invention improves the design and control of the micromirror array lens. This invention extends advantages and applications of the lens.